Due to perturbations in the Solar System, several hypothetical objects have been proposed.
Planet X/Tyche (1841-2014)Edit
Shortly after Uranus was discovered, astronomers noted "irregularities" in his orbital path. Thus began a hunt for a 12th planet (Ceres, Vesta, Pallas, and Juno were also considered planets at the time). In 1846, Johann Galle discovered Neptune, close to the position calculated by Urbain le Verrier. However, that wasn't the end of the story. Neptune wasn't massive enough to account for Uranus's funny orbit. In fact, Neptune itself seemed to be affected by a 9th planet. A search for a ninth planet was on, but only kicked into full gear when in 1894, Bostonian scientist Percival Lowell was convinced that Uranus and Neptune had funny orbits with a 9th planet, Planet X, pulling them off course. He died in 1916, without having discovered Planet X. However, his old observatory hired a young astronomer, Clyde Tombaugh to finish the search and Pluto was found in 1930. For 48 years, Pluto was blamed for the discrepancies. In 1972, Joseph Brady studied irregularities in the orbit of Halley's comet. proposed a Saturn sized planet with a period of 464 years with a retrograde orbit. This planet would explain the discrepencies in the orbits of Halley's comet. This gigantic trans-Plutonian planet was also searched for, but never found. . However, a number of scientists including planet X skeptics Alan Boss and Brian Marsden and planet X proponets Dale Cruishank, P. Kenneth Seidelmann, and Tom van Flanders attacked his claim, since a planet as big as Brady's would have severely affected the orbits of Saturn and Neptune and that Halley's comet changes his own trajectory by randomly ejecting jets of material. Astronomers still have not ruled out an Earth-sized planet at 36.2 AU, or 1 AU beyond Halley's aphelion, that would delay Halley's perihelion passage so that it agreed better with observations. However, should this world be found, it would be considered a dwarf planet by the current definition, since it will not have cleared its neighbourhood sufficiently. In 1978, James Christy and Robert Harrington found Charon, Pluto's main moon. This revised Pluto's mass down to 1/500 that of Earth. Afterwards, astronomers resumed the search for Lowell's Planet X, to no avail. Other astronomers proposed that it also was responsible for mass extinctions on Earth. Tom van Flanders said that a life killing planet X, if it exists, would tug on Saturn too, and that has not been observed. He and Harrington led multiple searches for Planet X in the 80s and 90s. van Flanders also examined the Neptunian satellite system. In 1987, Dan Whitmire and John Matese suggested a tenth planet at 80 a.u. with a period of 700 years and an inclination of perhaps 45 degrees (Tyche???), as an alternative to their "Nemesis" hypothesis. However, according to Eugene M. Shoemaker, this planet could not have caused those meteor showers that Whitmire and Matese suggested (see below). Later that year, John Anderson at JPL examined the motions of the spacecraft Pioneer 10 and Pioneer 11, to see if any deflection due to unknown gravity forces could be found. None was found -- from this Anderson concluded that a tenth planet most likely exists! JPL had excluded observations of Uranus prior to 1910 in their ephemerides, while Anderson had confidence in the earlier observations as well. Anderson concluded that the tenth planet must have a highly elliptical orbit, carrying it far away to be undetectable now but periodically bringing it close enough to leave its disturbing signature on the paths of the outer planets. He suggests a mass of five Earth masses, an orbital period of about 700-1000 years, and a highly inclined orbit. Its perturbations on the outer planets won't be detected again until 2600. In 1992, E. Myles Standish used data from the Voyager 2 flyby of Neptune to revise Neptune's mass down to an amount comparable to that of Mars. This showed that these discrepancies were solely caused by Neptune and an incorrect judgement of its mass. Astronomers called off the search of Planet X in Mid 1992.
However, that may not be the end of the story. The Kuiper Belt suddenly terminates at 48 AU. The number of space rocks like Pluto and Quaoar quickly decrease. As you can see, something is really going wrong here. Patryk Lykawka of Kobe University has claimed that the gravitational attraction of an unseen major planet, perhaps the size of Earth or Mars, might be responsible. To have any real affect on the Kuiper belt, this putative planet must lie between 50 and 72 AU and be between the mass of Earth and Mars and have an orbit and orbital period very similar to Harrington's tenth planet. Planet X should have a perihelion distance of at least 80 AU (1 AU is approximately the mean distance between the Earth and the Sun), a semimajor axis of 100-175 AU, and an orbital inclination of 32°. The planet would take 1,000-2,300 years to complete an orbit around the Sun. Furthermore, the mass of Planet X is estimated at 0.3-0.7 times the Earth's mass. If Planet X is near perihelion approach at a distance of about 80 AU, it could appear as bright as Pluto, with an apparent 14.8-20.3 magnitude. Worth noting, under these circumstances the planet would be detectable by future dedicated surveys. The planet's diameter would be 10,000-16,000 km, which is comparable to the size of the Earth. In summary, having the physical and orbital characteristics described above, Planet X would very probably fulfill the conditions of the IAU planet definition, and thus it would be considered a new planet in the solar system. She believes this planet formed between Uranus and Neptune, also similar to Harrington's Planet X. Lykawka subsequently used Harrington's ideas to bolster her claims. In 2013 and early 2014, it was proposed to use ranging data from the New Horizons spacecraft to constrain and eventually pin down the position of such a hypothesized body.[
Nemesis, the Sun's companion star (1983-present)Edit
Imagine that our Sun was not alone but had a companion star. Suppose that this companion star moved in an elliptical orbit similar to the Dwarf planets, its solar distance varying between 90,000 AU (1.4 light years) and 20,000 AU, with a period of 30 million years. Also suppose this star is dark or at least very faint, and because of that we haven't noticed it yet. This would mean that once every 30 million years that hypothetical companion star of the Sun would pass through the Oort cloud (a hypothetical cloud of proto-comets at a great distance from the Sun). During such a passage, the proto-comets in the Oort cloud would be stirred around. Some tens of thousands of years later, here on Earth we would notice a dramatic increase in the the number of comets passing the inner solar system. If the number of comets increases dramatically, so does the risk of the Earth colliding with the nucleus of one of those comets.
When examining the Earth's geological record, it appeared that about once every 30 million years a mass extinction of life on Earth has occurred. The most well-known of those mass events is, of course, the dinosaur extinction some 65 million years ago. The theory predicts there will be another mass extinction in 15 million years.
This hypothetical "death companion" of the Sun was suggested in 1985 by Daniel P. Whitmire and John J. Matese of the University of Southern Lousiana. It grew its legs from the Planet X theory (in the 80's John Anderson of the Jet Propulsion Lab suggested that our Sun has a binary companion that pulls Uranus and Neptune off course). It has even received a name, Nemesis. One awkward fact of the Nemesis hypothesis is that there is no evidence whatever of a companion star of the Sun. It need not be very bright or very massive. A star much smaller and dimmer than the Sun would suffice, even if it was a brown or a black dwarf (a planet-like body insufficiently massive to start "burning hydrogen" like a star). It is possible that this star already exists in one of the catalogues of dim stars without anyone having noted something peculiar, namely the enormous apparent motion of that star against the background of more distant stars (i.e., its parallax). If Nemesis should be found, few will doubt that it is the primary cause of periodic mass extinctions on Earth.
However, the existence of Nemesis is not very likely. The Infrared Astronomical Satellite (IRAS) examined the entire sky in the far infrared (IR) spectrum. However, it did not find any evidence of a star that would fit the description of "Nemesis." However, recent research no longer supports that extinctions of Earth happen at regular intervals, and thus the Nemesis theory is no longer needed. It is still reasonable, though, to blame Jupiter for killing the Dinosaurs by nudging an asteroid out of its orbit and into Earth.
Moons of Mars (1610-1877)Edit
The first to guess that Mars had moons was Johannes Kepler in 1610. When trying to solve Galileo's anagram referring to Saturn's rings, Kepler thought that Galileo had found moons of Mars instead.
In 1643, the Capuchin monk, Anton Maria Shyrl, claimed to have seen the moons of Mars. We now know that would be impossible with the telescopes of that time - probably Shyrl got deceived by a star nearby Mars.
In 1727, Jonathan Swift wrote in Gulliver's Travels about two small moons orbiting Mars, known to the Lilliputian astronomers. Their periods of revolution were 10 and 21.5 hours. Voltaire adopted these 'moons' in his 1750 novel Micromegas, the story of a giant from Sirius visiting our solar system.
In 1747, a German captain, Kindermann, claimed to have seen one moon of Mars, on July 10, 1744. Kindermann reported the orbital period of this Martian moon as 59 hours, 50 minutes, and 6 seconds.
In 1877, Asaph Hall finally discovered Phobos and Deimos, the two small moons of Mars. Their orbital periods are 7 hours, 39 minutes amd 30 hours, 18 minutes, quite close to the periods guessed by Jonathan Swift 150 years earlier.
None of these are true and were made either as a joke or a false alarm
The Nibiru cataclysm is a supposed disastrous encounter between the Earth and a large planetary object (either a collision or a near-miss) which certain groups believe will take place in the early 21st century. Believers in this doomsday event usually refer to this object as Planet X or Nibiru. The idea that a planet-sized object will collide with or pass by Earth in the near future is not supported by any scientific evidence and has been rejected as pseudoscience by astronomers and planetary scientists. It is widely believed that Nibiru will collide with Earth on December 21st, 2012. This started with a Wisconsin nutter by the name of Nancy Lieder. She claimed that as a little girl, aliens abducted her and put an implant in her brain. She warned that a large planetary object, Planet X, would pass through the Solar System destroying the Earth on May 2003. Also, it has been tied with Sitchin's Nibiru, although Sitchin put Nibiru's arrival at 2085. In 1999, New Age author/nutter V. M. Rabolu wrote in Hercolubus or Red Planet that Barnard's star is actually a planet known to the ancients as Hercolubus, which purportedly came dangerously close to Earth in the past, destroying Atlantis, and will come close to Earth again. Lieder subsequently used Rabolu's ideas to bolster her claims Barnard's star has been directly measured to be 5.98 ± 0.003 light years from Earth (35.15 trillion miles).While it is approaching Earth, Barnard's Star will not make its closest approach to the Sun until around 11,700 AD, when it will approach to within some 3.8 light-years. This is only slightly closer than the closest star to the Sun (Proxima Centauri) lies today. Since May 2003 passed without incident, several doomsayers connected the encounter with the 2012 doomsday scare. A Japanese cult called the Pana Wave Laboratory, which blocked off roads and rivers with white cloths to protect itself from electromagnetic attacks, also warned that the world would end in 2012 after the approach of a ninth planet.
Nibiru, Planet X, and Hercolobus have long been disproved by the one-way journeys of the Voyager 1 and Pioneer 10 space probes, now faster than any manmade object.
NASA jokingly proposed the name Caduceus, after the staff carried by the Roman god Mercury, during an April Fools' Day joke in which MESSENGER supposedly discovered a moon from Mercurial orbit. MESSENGER mission used the spacecraft to search for moons of Mercury in 2011 and 2013. As of 2012, MESSENGER mission had not conclusively observed any moon during multiple passes of Mercury, nor in its terminal orbit around the planet, although data collected in October 2013 is still being examined. The Mariner 10 mission also conducted a search. To date, no concrete evidence for a moon of Mercury has been observed.